A known transparent ABS resin is obtained by containing a graft copolymer obtained by copolymerization of rubbery polymer such as a diene rubber with (i) an aromatic vinyl compound such as styrene or α-methyl styrene, (ii) a vinyl cyanide compound such as acrylonitrile or methacrylonitrile, and (iii) an unsaturated alkyl carboxylate compound such as methyl methacrylate or methyl acrylate (as described in, for example, JP 2002-128848 A). This transparent ABS resin has good (i) transparency, (ii) mechanical strength balance such as impact resistance and rigidity, moldability and cost performance and is widely used for applications such as household electric appliances, communication equipment and general merchandises.
The following methods have been proposed as techniques of providing the transparency of the transparent ABS resin. For example, JP 2002-128848 A and JP 2003-277454 A propose methods that cause a difference in refractive index between an acetone insoluble component and an acetone soluble component of rubber-reinforced styrene resin to be less than 0.02. JP 2002-3548 A proposes a method that uses polybutadiene rubber, adjusts the refractive index of an acetone soluble component of a butadiene rubber-reinforced resin to 1.514 to 1.520, and causes a difference in refractive index between the acetone soluble component and an acetone insoluble component to be equal to or less than 0.006. JP 2002-212369 A proposes a method that adjusts a difference in refractive index between a rubbery polymer component and an acetone soluble component of a thermoplastic resin composition to be equal to or less than 0.03 and causes a difference in refractive index between the rubbery polymer and a graft component to be equal to or less than 0.03.
As a technique of providing the further higher transparency, JP 2014-181315 A proposes a method that specifies the transmittance at a wavelength of 700 nm and the transmittance at a wavelength of 450 nm by a spectrophotometer.
As a technique of improving the color tone of the transparent ABS resin, on the other hand, JP 2005-343946 A proposes a method that adds water to a graft copolymer (B) from a graft copolymer (B) feed conveyance unit in the process of manufacturing a vinyl (co)polymer (A) by continuous bulk polymerization or continuous solution polymerization of a vinyl monomer (a), subsequently supplying the graft copolymer (B) dehydrated and dried in advance from a side feeder to the vinyl (co)polymer in a molten state, and melt kneading the mixture to continuously manufacture a thermoplastic resin composition.
The above techniques, however, result in insufficient improvement of the transparency and the color tone. Accordingly, there are such problems that applications of the transparent ABS resin are limited and that molded products of the transparent ABS resin are darkened by bluing color toning.
It could therefore be helpful to provide a thermoplastic resin composition having significantly high transparency and good color tone, as well as excellent impact resistance.